A magnetic recording disc cartridge of the above type which is so called a floppy disc is composed of a flexible recording disc and a cover jacket for accommodating the recording disc within a chamber formed between a pair of square-shaped sheets of the jacket made of relatively hard material with a cleaning sheet interposed between the inner face of the outer sheet and the recording disc.
Such a magnetic recording disc cartridge has various advantages such, for example, the magnetic recording disc inside the jacket is not stained by dust in the outside atmosphere or magnetic powders since the recording disc can be loaded in a reproducing apparatus without removing the jacket and handling thereof is very simple.
However, a conventional magnetic recording disc cartridge has still various disadvantages due to the way of bonding the cleaning sheet to the outer sheet as mentioned hereinafter.
Such a magnetic recording disc cartridge will hereinafter be described in detail with reference to FIGS. 1 and 2 of the accompanying drawings.
The magnetic recording disc cartridge comprises a cover jacket 1 and a magnetic recording disc 2 contained therein. The magnetic disc 2 is formed by a base film made of plastic having flexibility and elasticity and has a central hole 3 for engagement with a drive shaft of a reproducing apparatus and a recording zone a presenting recording tracks.
The jacket 1 includes a generally rectangular outer sheet 4 made of synthetic resin material such as hard vinyl or polyester, and the outer sheet 4 has flaps 5A, 5B and 5C for heat bonding purpose. A cleaning sheet 6 made of non-woven cloth including thermoplastic fibers such as polyester fibers, nylon fibers or polypropylene fibers is placed on one side of the outer sheet 4 and thermally welded to the same to form linear weld patterns 7A, 7B and 7C.
In two pairs of square sheet portions 4A, 4B and 6A, 6B of the outer sheet 4 and the cleaning sheet 6 respectively, divided by a center line b, there are provided central windows 8 being larger in diameter than the central hole 3 of the magnetic disc for exposing the circular area of the disc around the periphery of the central hole 3, elongated head windows 9 for contact with an access head of a reproducing apparatus over the recording zone a of the magnetic disc 2 and index windows 10 for detecting a track starting point in the peripheral direction of the disc 2 and thereby determining the point of time for starting movement of the magnetic disc 2 in its diametrical direction for proper tracking.
Around the central windows 8 and the head windows 9 of the cleaning sheet 6, there are formed double or triple linear heat-bonding portions 11A and 11B along the peripheral portions of the windows 8 and 9 for preventing dropout of the filaments of the non-woven cloth.
The outer sheet 4 to which the cleaning sheet 6 is thermally bonded is bent along the center line b with the side having the cleaning sheet 6 inside, and the magnetic recording disc 2 is interposed between the square sheet portions 6A and 6B of the cleaning sheet 6. Then the flaps 5A, 5B and 5C are respectively bent along lines c to be bonded to the outer surface of one square sheet portion 4A of the outer sheet 4.
Since the non-woven cloth around the peripheries of the windows 8 and 9 of the cleaning sheet 6 are partially bonded with the outer sheet 4 by welding at the heat-bonding portions 11A and 11B in this magnetic recording disc cartridge, the cleaning effect in these portions are not spoiled and fluffing and dropout of the filaments are effectively prevented.
However, since the heat-bonding portions 11A and 11B are continuously formed around the windows 8 and 9 of the outer sheet, during the process of bonding the cleaning sheet and the outer sheet, the jacket is apt to be undesirably deformed due to the heat treatment whereby the circular peripheral edge portion of the jacket around the central window is slightly projected out of the plane of the major portion of the jacket.
Therefore, when the magnetic disc is inserted into the chamber of the jacket, the leading edge portion of the magnetic disc with respect to the direction of the insertion thereof is apt to be engaged with the projected portion, thereby preventing smooth insertion of the magnetic disc into the jacket, causing the magnetic disc to be crushed or damaged.
In addition, such deformation of the jacket reduces the commercial value of the magnetic disc cartridge.
Further, in the conventional magnetic recording disc cartridge, the trailing sides of the index windows 10 on the cleaning sheet 6 with respect to the direction of rotation of the magnetic recording disc 2 are not bonded to the outer sheets 4. Therefore, occasionally the filaments of the non-woven cloth on the trailing sides get fluffy by rotation of the magnetic recording disc 2 and tend to lie down toward the windows 10 or the non-woven cloth on the trailing sides is stretched by sliding contact with the disc 2 so as to gather around the windows 10. In such cases, detection sensitivity at the index windows 10 is lowered to cause errors in operation.